1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, and a facsimile machine, and more particularly, to an image forming apparatus that suppresses mutual adhesion of delivered sheets.
2. Description of the Related Art
Conventionally, there is known an image forming apparatus, such as a copier, a printer, and a facsimile machine, which uses an electrophotographic process and an electrostatic recording process. In the image forming apparatus of this type, an electrostatic latent image formed on a photosensitive drum serving as a latent image bearing member is subjected to a development process. Then, an unfixed toner image is formed on a sheet (transfer sheet, print sheet, photosensitive sheet, electrostatic recording sheet, or the like) by a transfer method or a direct method. Then, the toner image is fixed onto the sheet under the action of pressure and heat by a fixing device according to a variety of methods and configurations, which include a heat roller method, a film heating method, and an electromagnetic induction heating method. The sheet, on which the toner is fixed, is delivered by a pair of sheet delivery rollers to a sheet delivery tray thereafter, and is stacked thereon. At the time when the toner-fixed sheet is stacked on the sheet delivery tray, as measures against mutual adhesion and image deterioration of the sheets due to the toner affected by the heat, there is proposed an image forming apparatus which cools an upstream edge portion (hereinafter, referred to as a trailing edge portion), in a sheet delivery direction, of the stacked sheet on the sheet delivery tray (refer to US 2007/0196152). FIG. 10 illustrates a sheet delivery tray 301 of the conventional image forming apparatus.
On a wall surface of the sheet delivery tray 301, which is located upstream in the sheet delivery direction, multiple opening portions 302 are provided in a stack direction (height direction) of the sheets. The opening portions 302 allow air to be taken in, and enable contact between the sheets and the air. The air is fed along trailing edges of the stacked sheets, and cools the trailing edge portions of the stacked sheets.
As another cooling method, there is proposed a method in which the sheet, which is being delivered by a pair of sheet delivery rollers, is cooled by blowing air to a lower surface of the sheet (refer to Japanese Utility Model Application Laid-Open No. H04-44251). FIG. 11 illustrates an image forming apparatus including a conventional blower fan. As illustrated in FIG. 11, a blower fan 402 is installed between a pair of sheet delivery rollers 400 and a sheet delivery tray 401. Accordingly, the blower fan 402 blows the air to a lower surface of a sheet S, which is being delivered by the pair of sheet delivery rollers 400, and cools the lower surface of the sheet S which is passing above the blower fan 402.
In the conventional cooling method described above, when a sheet delivery speed is increased along with a speed-up of the image forming, the sheets are stacked one after another in a heat-accumulated state of not being cooled sufficiently. When the sheets are not cooled sufficiently, the sheets stacked on the sheet delivery tray are more likely to adhere to each other.
To be more specific, in the image forming apparatus illustrated in FIG. 10, the air is blown to the trailing edges of the sheets stacked on the sheet delivery tray. When the sheet delivery speed is increased, the sheets are stacked one after another before surfaces of the sheets, which are opposite to each other, are cooled sufficiently. As a result, such a state is brought where the heat is accumulated between the sheets, and accordingly, it is difficult to obtain a sufficient cooling effect, and the sheets are more likely to adhere to each other.
In the image forming apparatus illustrated in FIG. 11, when the sheet delivery speed is increased along with the speed-up of the image forming, a time during which each of the sheets passes through a blowing position of the blower fan is also shortened, and the sheets which are not cooled sufficiently are stacked on the sheet delivery tray one after another. As a result, the sheets stacked on the sheet delivery tray are more likely to adhere to each other.